php - how to filter catalog/category in magento -

i trying list of categories confine search query $searchstring 1 have filter products

$_productcollection = mage::getmodel('catalog/product')                     ->getcollection()                     ->addattributetosort('created_at', 'desc')                     ->addattributetoselect('*')                     ->setpagesize(20)                     ->addattributetofilter('name', array('like' => '%'.$searchstring.'%'))<---this line                     ->load(); 

but need filter categories .how can edit following code filter categories 1 above

$_helper = mage::helper('catalog/category'); $_categories = $_helper->getstorecategories(); if (count($_categories) > 0){     foreach($_categories $_category){         $_category = mage::getmodel('catalog/category')->load($_category->getid());         $_subcategories = $_category->getchildrencategories();         if($_category->getimageurl()!= ""){$categoryimage = $_category->getimageurl();}else{$categoryimage = "http://www.flintout.com/img/roughrock.jpg";}                   echo $categoryimage;                  echo $_category->getname();                  echo $_category->getdescription();          if (count($_subcategories) > 0){                             foreach($_subcategories $_subcategory){                 if($_subcategory->getimageurl()!= ""){$subcategoryimage = $_subcategory->getimageurl();}else{$subcategoryimage = "http://www.flintout.com/img/roughrock.jpg";}                   echo $subcategoryimage;                  echo $_subcategory->getname();                  echo $_subcategory->getdescription();              }         }     } } 

thanks